CASE REPORT

Management of interface irregularity due to high energy after uneventful SMILE

Ganesh, Sri MS, DNB; Brar, Sheetal MS

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JCRS Online Case Reports: October 2020 - Volume 8 - Issue 4 - p e00027
doi: 10.1097/j.jcro.0000000000000027
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Abstract

Interface problems such as haze, epithelial ingrowth, and deep lamellar keratitis, although less common with small-incision lenticule extraction (SMILE) than laser in situ keratomileusis (LASIK), nevertheless are reported.1 Most of these issues are seen after a complicated SMILE procedure, where there was difficulty in dissection because of opaque bubble layer/black spots/or inability to find the lenticule. However, interface irregularity after an uneventful SMILE procedure is rare and has not been reported. In this case report, we discuss the management of one such case that presented with suboptimal visual outcomes due to irregular interface resulting as a consequence of high laser energy, after an otherwise uneventful SMILE surgery.

CASE REPORT

A 48-year-old man was referred for opinion and management of suboptimal vision after a bilateral SMILE procedure performed 6 weeks previously for a low myopic refraction of −2.50/−0.25 @ 0 in the right eye and −1.75/−1.00 @150 in the left eye. The referring surgeon reported that the procedure was uneventful in both eyes, and there were no intraoperative complications, such as suction loss, lenticule stuck to cap, lenticule tears, or difficulty in dissection/extraction of the lenticule. However, the patient had blurred vision after the procedure in both eyes, which persisted at 6 weeks postoperatively, without much improvement with correction and despite the use of topical steroids and lubricants.

The patient reported that blurriness was present immediate postoperatively and was not associated with pain, redness, watering, or photophobia. On visual acuity testing, his uncorrected distance visual acuity (UDVA) was 6/12 in the right eye and 6/24 in the left eye, improving to 6/9p and 6/12 in the right eye and the left eye, respectively. His subjective refraction was −1.00 cyl @ 40 in the right eye and +0.50/−1.25 @ 160 in the left eye. Slitlamp examination showed a reasonably clear cornea without any interface haze in either of the eyes. Both eyes were quiet, with no conjunctival/ciliary congestion or anterior chamber reaction.

Corneal topography was performed using the Pentacam HR (Oculus Optikgeräte GmbH), which showed fairly regular keratometric (K) distribution (K1 42.5 diopter [D] and K2 44.0 D in the right eye and K1 42.7 D K2 44.1 D in the left eye) and flattening (Figure 1). Corneal higher-order aberrations (HOAs, root mean square) assessed using the Atlas topographer (Carl Zeiss Meditec), HOAs of 0.5 in the right eye and 0.6 in the left eye (Figure 2). However, OQAS (HD Analyzer, Visiometrics) showed objective scatter index (OSI) scores of 4 and 11.9 in the right and left eye, respectively, suggesting high intraocular scatter (Figure 3, A1 and B1). Both eyes were subjected to dilation and clinical photography with retroillumination using the Haag Streit photo slitlamp camera (model BX 900; Haag Streit Diagnostics, Zug, Switzerland). The clinical photographs revealed irregular interface quality in both eyes, which was rough, pitted, and showed the spiral pattern of laser delivery (Figure 4, A1 and B1). The severity of interface irregularity was more in the left eye than that in the right eye. Anterior segment optical coherence tomography (AS-OCT) (Optovue) also showed hyperreflectivity of the anterior corneal layers, corresponding to the area of the SMILE interface, suggesting a hazy interface in both eyes (Figure 5).

Figure 1.
Figure 1.:
After small-incision lenticule extraction, topography at 6 weeks postoperatively showing regular keratometry and uniform flattening in both eyes (A: right eye and B: left eye).
Figure 2.
Figure 2.:
After small-incision lenticule extraction, corneal HOAs measured using Atlas topographer (HOAs = higher-order aberrations; RMS = root mean square).
Figure 3.
Figure 3.:
OSI assessed using the high-definition analyzer 6 weeks after primary small-incision lenticule extraction (A1: RE, B1: LE), 3 months after phototherapeutic keratectomy repair surgery (A2: RE, B2: LE), and 3 months after enhancement (A3: RE, B3: LE) (LE = left eye; OSI = objective scatter index; RE = right eye).
Figure 4.
Figure 4.:
Clinical photographs taken in retroillumination after dilation showing the quality of interface 6 weeks after primary small-incision lenticule extraction (A1: RE, B1: LE), 3 months after phototherapeutic keratectomy repair surgery (A2: RE, B2: LE), and 3 months after enhancement (A3: RE, B3: LE) (LE = left eye; RE = right eye).
Figure 5.
Figure 5.:
After small-incision lenticule extraction, anterior segment optical coherence tomography of the (A) right eye (B) left eye showing evidence of haze in the anterior cornea corresponding to the corneal interface in both eyes.

On request, the primary surgeon shared the surgical videos and treatment planning of the SMILE surgery of both eyes for review. Surgical videos of both eyes, however, did not reveal any abnormal bubble pattern or intraoperative complications/difficulty in tissue dissection (Video 1, available at http://links.lww.com/JC9/A5 and Video 2, available at http://links.lww.com/JC9/A6, showing the primary SMILE surgery in the right and left eye, respectively).

Figure 6 shows the laser parameters used to perform the primary SMILE procedure for both the eyes. All treatment parameters were within the acceptable range, except that a cut energy index of 40, corresponding to an energy of 200 nJ was used, which appeared to be on the higher side of the recommended range. Spot and track separation used for both eyes was 4.5 µm. The surgeon reported using the same energy settings for his previous few SMILE cases or so, without any intraoperative or postoperative visual recovery issues. However, it appeared that this energy setting was a bit high for this patient, considering the recent trend of using low energies and its association with faster visual recovery after SMILE.2 Based on the preoperative treatment parameters and postoperative AS-OCT and clinical findings, a diagnosis of irregular interface as a result of high-energy settings of the femtosecond laser was made.

Figure 6.
Figure 6.:
Treatment planning used during the primary SMILE surgery for both eyes (SMILE = small-incision lenticule extraction).

In view of the above findings, a decision to perform repair surgery on both eyes with CIRCLE software–enabled flap creation and phototherapeutic keratectomy (PTK) to smoothen the rough interface was made. Chances of hyperopic shift as a consequence of the repair procedure were explained to the patient.

In both eyes, CIRCLE software Pattern “C” was used to create the flap with a nasal hinge, at a depth of 130 µm, which was same as the cap thickness of the original SMILE procedure. After separating and lifting the flap with a blunt dissector, a PTK procedure was performed with a 50 µm ablation depth and 7 mm treatment zone, using the MEL-90 excimer laser platform (Carl Zeiss Meditec) (Video 3, available at http://links.lww.com/JC9/A7 showing the repair surgery of the right eye, and the similar procedure was performed for the left eye). The interface was washed with a balanced salt solution, followed by flap reposition. Postoperatively, the patient was prescribed ofloxacin eyedrops 0.3% (Exocin) 4 times for 3 days, prednisolone acetate eyedrops 0.1% (Pred Forte) 4 times a day for 10 days, and lubricants 4 times for 4 weeks or more.

Three months after repair surgery, his UDVA improved to 6/12 in the right eye and 6/12p in the left eye. His subjective refraction in the right eye was +0.25/−1.00 @ 40, which improved the corrected distance visual acuity (CDVA) to 6/6. The left eye accepted a correction of +1.00/−1.25 @ 145; however, the CDVA in this eye did not improve beyond 6/12p. There was also an improvement in the interface quality, which appeared to be smoother and less rough compared with the prerepair clinical photographs (Figure 4, A2 and B2). However, his corneal HOAs increased from 0.5 to 1.1 in the right eye and 0.6 to 1.6 in the left eye (Figure 7).

Figure 7.
Figure 7.:
Three months after phototherapeutic keratectomy repair surgery, corneal HOAs measured using Atlas topographer (HOAs = higher-order aberrations; RMS = root mean square).

Considering that the patient had undergone laser treatment twice in the past 3 months in both eyes, the potential risks of further treatments, especially a higher possibility of haze formation, were discussed with the patient, and therefore, he was advised to use spectacles for improving vision. The patient, however, insisted on a repeat procedure for the correction of refraction and enhancement of his vision, while understanding the possible risks and benefits of the enhancement surgery.

Because there was an improvement in the CDVA in both eyes, a flap relift followed by the topography-guided LASIK procedure to correct the residual refraction in both eyes under guarded visual prognosis was attempted. Figure 8 shows the treatment planning of the enhancement surgery for both the eyes. Three months after enhancement, he recovered a full UDVA of 6/4.5 in the right eye and did not accept any correction. The left eye had a UDVA of 6/9p, and there was a minor improvement in the CDVA (6/9p), with a correction of +0.5/−1.0 @ 160. The final appearance of interface (Figure 4, A3 and B3) still showed some amount of roughness in both the eyes, although it was remarkably better compared with what it was at the time of initial presentation (Figure 4, A1 and B1). On the last follow-up, the OSI values had recovered in the right eye from 4.0 to a normal value of 0.9. However, in the left eye, it was still high (2.8), although it was better compared with prerepair surgery (11.9) (Figure 3, A2 and B2). His corneal HOAs also reduced from 1.1 to 0.5 in the right eye and 1.6 to 0.7 in the left eye (Figure 9). The patient was satisfied with the enhancement results and was able to manage his activities without spectacles, despite a loss of one line of the CDVA in the left eye.

Figure 8.
Figure 8.:
Treatment planning used for enhancement surgery with topography-guided laser in situ keratomileusis using the MEL 90 excimer laser for both eyes.
Figure 9.
Figure 9.:
Three months after enhancement with topography-guided laser in situ keratomileusis, corneal HOAs measured using Atlas topographer (HOAs = higher-order aberrations; RMS = root mean square).

No flap-related complications (rupture, perforation, and miscreation) occurred, and no CIRCLE software–related issues (debris in the interface) occurred in either eye during the repair or enhancement procedures.

DISCUSSION

This case highlights several points, which may be of practical importance to refractive surgeons performing SMILE. As described earlier, the CIRCLE software is a dedicated software in the VisuMax femtosecond laser system, which enables the conversion of SMILE cap into a flap, to allow the surgeon to perform excimer laser–assisted enhancement for any refractive inaccuracies.3 However, its use for therapeutic indications arising out of complicated SMILE scenarios has not been explored much. Recently, we demonstrated the utility of this software in managing retained lenticules or their fragments arising out of complicated SMILE situations.4 In this case report, we describe a unique complication of interface irregularity after uneventful SMILE, occurring due to the use of high energy for treatment planning and successfully managed using the CIRCLE software.

It is known that the mechanism of photodisruption induced by the femtosecond laser system produces plasma, shock wave, and cavitation bubbles to create a cleavage plane in the cornea.5 When applied to SMILE, the low-energy profile, reduced pulse duration, and high laser firing speed, provided by the femtosecond laser platform, result in a reduced cavitation bubble size and breakdown threshold of plasma formation, therefore minimizing collateral damage and tissue inflammation.6

Donate et al. in 2016 first studied the correlation of the energy cut index and visual recovery after SMILE, where they compared the safety, efficacy, predictability, and ocular optical quality outcomes between the standard energy group (164 eyes) using a laser cut energy index of 36 (180 nJ) and the plasma threshold group (322 eyes) using a cut energy index of 20 (100 nJ, close to the plasma threshold). The results showed that an energy level close to the plasma threshold during SMILE provided a faster and better visual recovery.2 Followed by this, many studies have demonstrated similar results in terms of the energy and visual recovery after SMILE.

Recently, Yong et al. studied the effect of lowering femtosecond laser energy on the surface quality of the intrastromal interface during SMILE and concluded that lowering laser energy levels can improve the surface quality of the lenticule of SMILE. They further recommended to reduce the laser energy to less than 115 nJ at a spot separation of 4.5 μm to achieve better visual outcomes with faster recovery after the procedure.7 Another large cohort retrospective study published recently also suggested that the lower end of the energy settings was associated with a better postoperative UDVA with SMILE, and that a spot-track-distance of 4.5 μm with 125 nJ energy was the optimal combination within this range.8 In the light of above studies, it appears that the femtosecond laser energy settings (200 nJ) used in the present case, during the primary surgery, were relatively high and yet to be optimized. Moreover, the patient was much older (48 years) and, thus, the corneal biomechanics being comparatively stronger with stiffer collagen tissue, the use of high energy probably leads to greater disruption of the collagen fibrils, resulting in increased roughness and irregularity of the interface.9 This leads to a near-permanent enhanced interface visibility because of the spiral laser pattern–associated roughness and increased inflammatory response, which is usually a transient phenomenon.10 In our experience, reducing the energy to approximately 150 μm with a closer spot spacing of 4 to 4.2 μm could have resulted in a smoother lenticule planes and also the postoperative interface.

In this context, interface quality assessment using dilated clinical photography with retroillumination, by the method earlier described by us, may be particularly useful, as diagnostic methods of topography and aberrometry may not aid much in diagnosis, as in this case.11 AS-OCT, however, may provide supportive evidence, although it may not be sensitive enough in early cases of interface-related issues after SMILE. The OSI, provided by a double-pass system, would usually show high values because of increased scatter and may be a more sensitive tool in such situations.12

Management of these cases remains challenging, as the outcomes may be unpredictable with further laser treatments, due to the risk of increased haze formation. Results of topography-guided ablations as primary repair treatments may not result in favorable outcomes, unless the interface quality is improved. Hence, first, a PTK treatment to smoothen the interface may be required, which may be subsequently followed by a more specific topography-guided treatment directed toward the correction of the refractive error and reduction in the HOAs.

This case also highlights the importance of energy optimization in SMILE and careful treatment planning with respect to selection of energy parameters, especially while treating older patients whose corneal biomechanics are different compared with younger individuals.13 Also, while treating low myopia, as in the present case, it may be suggested to increase the peripheral thickness of the lenticule to up to 25 to 30 µm and use larger optical zones, which would increase the distance between the cap and the lenticule cuts, thus minimizing tissue distortion and potentially improving visual outcomes.14

In our previously published study, correlating interface healing with visual recovery, we have shown that the corneal interface may take up to 3 to 4 months for healing.11 Considering this, the timing of repair surgery, ie, PTK, which was performed at 6 weeks in the present case, may be debatable. It may have been ideal to wait for 3 months or so before contemplating the repair surgery. However, because the purpose of the repair treatment was therapeutic and not refractive, this may be justified.

Nevertheless, to our knowledge, this is the first case reporting the outcomes of management of interface irregularity after uneventful SMILE surgery, successfully managed using CIRCLE software–enabled flap creation and PTK, followed by sequential enhancement with topography-guided LASIK, resulting in satisfactory visual outcomes. These complicated cases, however, require thorough preoperative evaluation to guide proper decision making and detailed discussion with the patient, regarding the pros and cons of retreatments for best possible outcomes.

WHAT WAS KNOWN

  • Optimized and lower energy settings result in uniform laser delivery and smooth tissue dissection and interface quality in SMILE surgery.

WHAT THIS PAPER ADDS

  • Use of relatively higher energies (>175 nJ) may potentially result in interface irregularity, especially in older individuals with stronger corneal biomechanics. In these cases, reducing the energy to approximately 150 μm with a closer spot spacing of 4 to 4.2 μm might result in creation of smoother lenticule planes and the corneal interface.

REFERENCES

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11. Ganesh S, Brar S, Pandey R, Pawar A. Interface healing and its correlation with visual recovery and quality of vision following small incision lenticule extraction. Indian J Ophthalmol 2018;66:212–218
12. Saad A, Saab M, Gatinel D. Repeatability of measurements with a double-pass system. J Cataract Refract Surg 2010;36:28–33
13. Celebi ARC, Kilavuzoglu AE, Altiparmak UE, Cosar Yurteri CB. Age-related change in corneal biomechanical parameters in a healthy Caucasian population. Ophthalmic Epidemiol 2018;25:55–62
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